Throughout this application, various publications are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosure of these publications in their entireties are hereby incorporated by reference herein to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein.
Epidemiological and experimental evidence has shown that consumption of diets high in certain vegetables, such as cabbage and other members of the family Cruciferae, may reduce the incidence of certain cancers. These vegetables typically contain dithiolthiones, which are sulfur-containing compounds that have been associated with a number of biochemical changes. The most notable of these changes include increases in the activities of enzymes catalyzing the inactivation of toxic compounds, including carcinogens, and increases in tissue reduced glutathione (GSH) levels (10). Certain synthetic dithiolthiones, for example substituted 1,2-dithiol-3-thiones, are also known to be useful medicinally as antischistosomal agents, choleretics, and to stimulate salivary secretion (6, 8, 10). The preparation and use of such compounds as pharmaceutical compositions is described, for example, in U.S. Pat. No. 4,138,487, the disclosure of which is incorporated herein by reference in its entirety.
Oltipraz (5-(2-pyrazinyl)-4-methyl-1,2-dithiol-3-thione) is a synthetic dithiolthione with physiochemical properties similar to those of dithiolthione antioxidants typically found in cruciferous vegetables (6). Based upon these properties, Oltipraz, and other 1,2-dithiol-3-thione derivatives have been studied for use as potential chemopreventive agents (10-15). Chemoprevention refers to the use of natural or synthetic agents to inhibit carcinogenesis. The development of chemopreventive agents is focused on identifying agents that prevent or inhibit the intracellular changes that may induce tumor formation or lead to the formation of pre-neoplastic lesions. This may be contrasted with the development of chemotherapeutic agents, which is focused upon identifying agents that may lead to the regression of existent neoplasms, and/or prevent the further growth or metastasis of tumors. Chemopreventive agents may work, for example, to detoxify carcinogenic compounds, or to protect genetic material from changes that may be associated with the initiation of cancer. Preclinical evaluation of Oltipraz has demonstrated its broad efficacy in preventing carcinogen-induced rodent tumors in multiple organ sites, including the breast, bladder, colon, stomach, liver, lymph nodes, lung, pancreas, and skin (6, 7). Clinical studies on the initial use of Oltipraz as an anti-schistosomal agent (8), and in more recent phase I and II trials in patient populations susceptible for cancer of the colon, breast, liver, and lung (reviewed in Ref. 7), have also revealed its minimal toxicity in man.
The significant chemopreventive activity of Oltipraz in vivo (7) and in vitro (9) has been attributed primarily to its pronounced induction of a battery of phase II detoxification enzymes (10-13) and its activity in decreasing the formation of DNA-carcinogen adducts in vitro and in vivo (11, 14-16). Most of the chemoprevention protocols tested to date have involved concomitant exposure of the test subject to both carcinogen and Oltipraz (6). Complete protection against aflatoxin B1 has been achieved when Oltipraz is fed both before and during carcinogen administration. However, administration of the drug after exposure to aflatoxin B1 was observed to have no chemopreventive effect (6). The prevention of initiation of azoxymethane-induced colon carcinogenesis by Oltipraz has been shown to be nearly equi-effective, regardless of whether the drug was administered during or after carcinogen administration, further suggesting that Oltipraz may inhibit the induction of cancer by more than one mechanism.
To date, little if any evidence exists to suggest that substituted 1,2-dithiol-3-thiones such as Oltipraz may be useful as chemotherapeutic agents for treating neoplastic conditions, however. Although it has been shown in the Syrian hamster model of N-nitrosobis(2-oxopropyl)-amine (BOP)-induced ductal pancreatic carcinoma that concurrent administration of BOP and Oltipraz may lead to a prolonged survival rate in animals that develop BOP-induced metastatic disease (7), there has previously been no evidence to suggest that compounds such as Oltipraz may be used therapeutically to inhibit tumor growth or metastasis, or to induce regression of established tumors.
Angiogenesis, the formation of new blood vessels out of pre-existing capillaries, is a sequence of events that is of key importance in a broad array of physiologic and pathologic processes. Normal tissue growth, such as in embryonic development, wound healing, and the menstrual cycle, is characterized by dependence on new vessel formation for the supply of oxygen and nutrients as well as removal of waste products. A large number of different and unrelated diseases are also associated with formation of new vasculature. Among certain pathologies are conditions in which angiogenesis is low, and should be enhanced to improve disease conditions. More frequently, however, excessive angiogenesis is an important characteristic of various pathologies, including pathologies characterized or associated with an abnormal or uncontrolled proliferation of cells. Pathologies which involve excessive angiogenesis include, for example, cancer (both solid and hematologic tumors), cardiovascular diseases (such as atherosclerosis and restenosis), chronic inflammation (rheumatoid arthritis, Crohn's disease), diabetes (diabetic retinopathy), psoriasis, endometriosis, neovascular glaucoma and adiposity (3). These conditions may benefit from chemotherapeutic inhibition of angiogenesis.
Generally speaking, the angiogenic process entails the proliferation and migration of a normally quiescent endothelium, the controlled proteolysis of the pericellular matrix, and the synthesis of new extracellular matrix components by developing capillaries. The establishment of new intra- and intercellular contacts and the morphological differentiation of endothelial cells to capillary-like tubular networks provide support for their subsequent maturation, branching, remodeling and selective regression to form a highly organized, functional microvascular network. The autocrine, paracrine and amphicrine interactions of the vascular endothelium with its surrounding stromal components, as well as with the pro-angiogenic and angiostatic cytokines and growth factors orchestrating physiologic angiogenesis, are normally tightly regulated both spatially and temporally (1-4).
Angiogenesis is crucial to the growth of neoplastic tissues (4). For more than 100 years, tumors have been observed to be more vascular than normal tissues. Several experimental studies have suggested that both primary tumor growth and metastasis require neovascularization (1). In contrast to the well orchestrated process described above for normal tissue growth, the pathologic angiogenesis necessary for active tumor growth is generally sustained and persistent, with the initial acquisition of the angiogenic phenotype being a common mechanism for the development of a variety of solid and hematopoietic tumor types (1-4). Tumors that are unable to recruit and sustain a vascular network typically remain dormant as asymptomatic lesions in situ (4). Metastasis is also angiogenesis-dependent: for a tumor cell to metastasize successfully, it generally must gain access to the vasculature in the primary tumor, survive the circulation, arrest in the microvasculature of the target organ, exit from this vasculature, grow in the target organ, and induce angiogenesis at the target site. Thus, angiogenesis appears to be necessary at the beginning as well as the completion of the metastatic cascade (4).
The criticality of angiogenesis to the growth and metastasis of neoplasms thus provides an optimal potential target for chemotherapeutic efforts. Appropriate anti-angiogenic agents may act directly or indirectly to influence tumor-associated angiogenesis either by delaying its onset (i.e., blocking an “angiogenic switch”) or by blocking the sustained and focal neovascularization that is characteristic of many tumor types. Anti-angiogenesis therapies directed against the tumor-associated endothelium and the multiple molecular and cellular processes and targets implicated in sustained pathologic angiogenesis are being actively evaluated for their safety and efficacy in multiple clinical trials (reviewed in Ref. 1, 4 and 5). However, there has been limited success to date with the discovery and/or identification of safe and/or effective anti-angiogenic agents.
Accordingly, new and/or better anti-angiogenic agents and/or methods for inhibiting angiogenesis are needed. The present invention is directed to these, as well as other, important ends.